Field of the Invention
The present invention relates to a dust cover for a ball joint.
Further, the present invention relates to a dust cover for a ball joint which is used in an automobile suspension device, and a steering device.
Description of the Conventional Art
Conventionally, as a ball joint to which a dust cover is installed for the purpose of a dust prevention and a water prevention in a ball joint coupling portion, there has been known a dust cover for a ball joint which is described in FIG. 5 (Japanese Unexamined Patent Publication No. 62-137408).
In a seal structure of this kind of ball joint dust cover, a spherical head portion 200 formed in one end of a ball stud 100 is retained within a socket 300.
Further, a shaft 400 in the other end of the ball stud 100 is fastened and fixed to a knuckle 500.
On the other hand, a one end large-diameter opening portion 800 formed into an approximately C-shaped cross section of a dust cover 600 made of an elastic material is fitted and retained into an annular groove portion 310 which is formed in an outer peripheral surface of the socket 300 by an annular presser bar ring 700, and the other end small-diameter opening portion 150 in which a metal reinforcing ring formed into an L-shaped cross section is embedded is retained to the shaft 400. Further, a rubber existing between the metal reinforcing ring and the shaft 400 is appropriately compressed, and a sealing performance is achieved in relation to an oscillating motion of the ball stud 100 on the basis of a repulsive force (a tension force) and a following property of the rubber.
However, when this kind of conventional dust cover 600 made of the elastic material oscillates in a state in which the ball stud 100 is inclined as shown in FIG. 5, a force elongating the small-diameter opening portion 150 is applied to the dust cover 600 in a side where a film portion of the dust cover 600 made of the elastic material extends (a right side on the drawing). As a result, there is generated a so-called opening phenomenon of the small-diameter opening portion 150 is generated so that contact between a lip portion of the small-diameter opening portion 150 and the knuckle 500 is disengaged.
As a result, a sealing performance in the small-diameter opening portion 150 is lowered, and there has been a problem that earth and sand or refuse enters into the dust cover 600.
Particularly, the rubber constructing the dust cover 600 made of the elastic material loses its elasticity under a low-temperature atmosphere, and a following property of the film portion to the oscillating motion of the ball joint is lowered. As a result, it has been known that an opening phenomenon that the seal lip portion moves away from the shaft 400 is significantly generated.
Further, in the case that the opening phenomenon mentioned above is generated, not only the earth and sand or the refuse enters into the dust cover 600 from an external portion, but also there has been brought about a danger that grease sealed within the dust cover 600 leaks out.
As a countermeasure for reducing the opening phenomenon mentioned above, there has been proposed a dust cover for a ball joint which intends to improve the sealing performance against the oscillating motion of the ball stud by installing a retainer to a shaft side of the ball stud, however, this countermeasure is not sufficient (Japanese Unexamined Utility Model Publication No. 4-4520).